This invention relates generally to active rectifier circuits and more particularly to an improved averaging type AC to DC converter.
Prior art active rectifier circuits incorporate a complementary diode pair in a negative feedback loop. The loop gain decreases the non-linear effect of the diode switching but must be less than unity at 180.degree. phase shift to avoid unstable feedback. This is accomplished by the use of a compensation capacitor across a stage of the amplifier to introduce a dominant pole. This technique purposely reduces loop gain at higher frequencies but additionally decreases the maximum slew rate of the output.
Prior art active rectifier circuits therefore suffer from two limitations. First, the gain must be decreased for feedback stability, thus adversely affecting the detection and accurate rectification of small signals. Second, the decreased slew rate of the output adversely affects the accurate rectification of large and/or high frequency signals.
Accordingly, the principal objects of this invention are to increase the gain for small signals, to increase the slew rate of the output, and to avoid unstable feedback. Other and incidental objects of the present invention will become apparent from a study of the following detailed description.
These objects are accomplished in accordance with the preferred embodiment by activating the known compensating feedback loop only when one of the complementary rectifying diodes is on and by allowing the amplifier to run `open loop` during diode switching. The compensation feedback loop is split into two alternate loops in the present invention, each loop incorporating one of the complementary rectifying diodes and a gain reducing capacitor. The incorporation of the diodes in the alternate feedback loops effectively opens the compensation feedback loop when the diodes are switching, thus significantly increasing the gain when detecting small signals and simultaneously increasing the slew rate of the output for accurate rectification of large and/or high frequency signals.